Dinosaur why extinct

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By Sam Rae and Lisa Hendry. What caused the Cretaceous extinction? Read more about what caused the extinction of the dinosaurs. Climate change Feature Extinction Prehistoric Dinosaurs. Discover dinosaurs Find out what Museum scientists are revealing about how dinosaurs looked, lived and behaved. Dig up dino facts. Dino Directory Explore more than dinosaurs by name, shape or when and where they lived.

What was the ocean like when dinosaurs roamed the Earth? Ancient forests seem to have flamed out across much of the planet. And while some mammals, birds , small reptiles, fish , and amphibians survived, diversity among the remaining life-forms dropped precipitously. In total, this mass extinction event claimed three quarters of life on Earth. For now, two leading ideas are battling it out within the scientific community: Were dinosaurs victims of interplanetary violence, or more Earthly woes?

One of the most well-known theories for the death of the dinosaurs is the Alvarez hypothesis, named after the father-and-son duo Luis and Walter Alvarez. In , these two scientists proposed the notion that a meteor the size of a mountain slammed into Earth 66 million years ago, filling the atmosphere with gas, dust, and debris that drastically altered the climate. Iridium is relatively rare in Earth's crust but is more abundant in stony meteorites, which led the Alvarezs to conclude that the mass extinction was caused by an extraterrestrial object.

At about 93 miles wide, the Chicxulub crater seems to be the right size and age to account for the dino die-off. In , scientists drilled a rock core inside the underwater part of Chicxulub , pulling up a sample stretching deep beneath the seabed. This rare peek inside the guts of the crater showed that the impact would have been powerful enough to send deadly amounts of vaporized rock and gases into the atmosphere, and that the effects would have persisted for years.

And in , paleontologists digging in North Dakota found a treasure trove of fossils extremely close to the K-Pg boundary , essentially capturing the remains of an entire ecosystem that existed shortly before the mass extinction.

Tellingly, the fossil-bearing layers contain loads of tiny glass bits called tektites—likely blobs of melted rock kicked up by the impact that solidified in the atmosphere and then rained down over Earth. However, other scientists maintain that the evidence for a massive meteor impact event is inconclusive, and that the more likely culprit may be Earth itself.

Ancient lava flows in India known as the Deccan Traps also seem to match nicely in time with the end of the Cretaceous, with massive outpourings of lava spewing forth between 60 and 65 million years ago. Today, the resulting volcanic rock covers nearly , square miles in layers that are in places more than 6, feet thick.

Proponents of this theory point to multiple clues that suggest volcanism is a better fit. Other research has found evidence for mass die-offs much earlier than 66 million years ago, with some signs that dinosaurs in particular were already in a slow decline in the late Cretaceous. This all makes sense, supporters say, if ongoing volcanic eruptions were the root cause of the world-wide K-Pg extinctions. Increasingly, scientists trying to unravel this prehistoric mystery are seeing room for a combination of these ideas.

That might seem strange. But the connection is still there, all the way down to the bone. About million years ago, in the Jurassic, the first birds evolved from small, feathery, raptor-like dinosaurs, becoming another branch on the dinosaur family tree. For more than 80 million years, birds of all sorts flourished, from loon-like swimmers with teeth to beaked birds that carried streamer-like feathers as they flew.

With hindsight, birds can be categorized as avian dinosaurs and all the other sorts—from Stegosaurus to Brontosaurus —are non-avian dinosaurs. The entire reason paleontologists make that split is because of a catastrophe that struck 66 million years ago.

Some of the debris thrown into the atmosphere returned to Earth, the friction turning the air into an oven and sparking forest fires as it landed all over the world. Then the intensity of the heat pulse gave way to a prolonged impact winter, the sky blotted out by soot and ash as temperatures fell.

The geologic break between the two is called the K-Pg boundary, and beaked birds were the only dinosaurs to survive the disaster. The end of the Cretaceous boasted an entire array of birds and bird-like reptiles. But of these groups, it was only the beaked birds that survived. The happenstances of evolution had given birds a lucky break, the key events set in motion long before the asteroid struck. The very first bird, the million-year-old Archaeopteryx , initially confounded 19th century naturalists because it had teeth.

For tens of millions of years after Archaeopteryx , toothed birds continued to thrive and evolve alongside their dinosaurian relatives.